1. Field of the Invention
The present invention relates to a storage system and data management method that is particularly appropriate for application to storage systems ensuring reliability and fault tolerance for stored data.
2. Description of Related Art
In the related art, a method of managing a plurality of hard disks using a RAID (Redundant Array of Independent/Inexpensive Disks) exists for storage systems managing data using storage apparatus. At least one or more logical volumes (hereinafter referred to as “logical volumes”) are formed on a physical storage region provided by a large number of hard disks.
Of the RAID methods, for example, a method referred to as RAID1 exists to ensure that data is not lost from the host apparatus even if one hard disk fails. In this method, the host apparatus accesses one virtual logical volume (hereinafter referred to as “virtual volume”) but in reality adopts a method where the same data is stored on respective hard disks constituted by two hard disks. According to this method, it is possible to ensure data redundancy.
Further, other technology for providing data redundancy is disclosed in patent document 1 where technology is provided where a module is equipped with a plurality of data storage sections comprised of slice regions formed in advance in order to store sliced data, a management information storage section for managing the slice regions, and a communication function section for communicating sliced data stored in the data storage sections and management information for storing within the management information section.
On the other hand, technology referred to as a so-called AOU (Allocation On Use) function where virtual volumes are supplied to a host apparatus without making logical volumes of fixed capacities from storage regions of a hard disk and where storage regions of a hard disk are dynamically allocated to virtual volumes according to requests from the host apparatus is also proposed. According to technology using this AOU function, it is possible to dynamically extend the capacity of a virtual volume.
[Patent Document 1]
International publication pamphlet number 2004/104845
However, with the RAID 1 method referred to as mirroring, two hard disks are written to at the same time when data is written to a virtual volume. This means that the hard disk of the smaller capacity has to be catered for in the event that the capacity of the two hard disks is different.
Further, on the other hand, in the event that a fault occurs where functioning as a RAID group no longer takes place, with a storage system that does not utilize an AOU function, it is no longer possible to use logical volumes belonging to this group, but with storage systems utilizing an AOU function, it is no longer possible to use virtual volumes where regions are allocated from the RAID group. There is therefore the problem that storage systems utilizing an AOU function exert substantial influence on the system as a whole compared with storage systems that do not utilize and AOU function.
The present invention therefore sets out to provide a storage system and data management method that utilizes an AOU function and improves reliability and fault tolerance of a hard disk saving data.